1. Field of the Invention
The present invention relates to a rope system and more particularly, an endless rope which is arranged to travel through a machine while being tensioned in its longitudinal direction.
2. Description of the Related Art
In conventional rope systems, sometimes there is a danger that a rope gets stuck or that a rope is inadvertently wrapped around a drying cylinder or around a roll. This may result in serious damage to the equipment, e.g. to the rope tensioning device or to other elements of the rope system.
In the paper technology, in particular in paper or cardboard making machines or in paper or cardboard finishing machines, a rope system is often used for threading the paper or cardboard web into the machine (in particular into the drying section) when the machine is started up or after a web break. Basically, two (sometimes three) endless ropes are used which travel together along the web travel path through a drying section, a calendar section or a coating section. At the upstream end of a section, the two ropes form a rope nip. At this point, the ropes grip the beginning of an edge strip (a so-called xe2x80x9ctailxe2x80x9d) of the paper or cardboard web and transfer the edge strip through the section.
What is needed in the art is a rope system wherein the potential of damage to the equipment is eliminated or at least reduced.
The present invention provides a rope system and method for using a rope system that includes a measuring device for measuring the tension value in at least one endless rope. Preferably, the tension value is measured continuously during operation of the machine.
The measuring device is adapted to detect excessive tension, which is above the desired tension value normally maintained in the rope. Excessive tension may appear if the rope gets stuck or if other damage occurs to the rope system.
According to one embodiment of the invention, a rope cutter is provided for severing the endless rope if the rope suddenly is excessively tensioned. The rope cutter becomes immediately active when excessive tension is detected.
Generally, after severing the rope, the paper making machine is able to continue operating in the normal way because any danger of damage to the machine has been eliminated. Certainly, some loss arises from severing the rope. However, this loss is inconsequential in comparison to the damage that would occur to the mechanical equipment if the rope was not cut.
Preferably, the rope system of the present invention includes a rope tensioning device with a cylinder which is adapted to move at least one sheave, that is wrapped by the rope, for tensioning the rope. A selected pressure will be supplied to the cylinder which corresponds to the desired tension value. The measuring device is adapted to measure the prevailing pressure in the cylinder. The measuring device may be embodied as a pressure switch which creates a signal if the pressure in the cylinder exceeds the selected pressure. That signal will then be transmitted to the rope cutter.
In one embodiment of the invention, the rope cutter includes a cylinder for actuating the rope cutter. A control valve may be provided to control the cylinder such that the cylinder actuates the rope cutter when the signal exists. In a preferred embodiment of the invention, the control valve is controlled by a pressure fluid (e.g. compressed air) which is admitted to the control valve when the signal exists.